The present invention relates to a diamond coated body for which the diamond layer is smoothened which increases its wear and flaking resistance, in particular to be used as a cutting tool for cutting Al-alloys containing e.g. Si and Cu as alloying elements and the like.
After many years of research efforts, the production of thin layers of diamond directly from the gas phase by CVD plasma technique for coating of cutting tools has been realized. Gas phase deposition of diamond on cemented carbide tools has been assessed by a variety of methods where the tailoring of the cemented carbide has proven to be of great importance.
The predominant growth manner for CVD plasma diamond layers is that the grain size grows markedly with deposition time. Typically, for a 6-10 .mu.m thick diamond layer, the diamond grain size is 2-5 .mu.m giving a surface roughness in this regime. One way to avoid the increase in grain size by growth time is to apply a bias voltage onto the tools which gives a smooth diamond surface but with the risk of achieving a deteriorated diamond quality. Besides, large scale production involving biasing puts demands on careful and hence more elaborate fixturing.
Smoothening of the diamond layers is generally regarded as being beneficial in cutting applications since the cutting forces are reduced upon lowering the coefficient of friction. Measurements of the coefficient of friction have shown that a much lower value is obtained for a polished CVD diamond layer compared to an as-deposited layer. A method for achieving a smooth diamond layer on cutting tools is mechanical polishing but due to the three-dimensional and often complicated shape, the polishing has only been possible to apply on flat rake surfaces or on a small part of the flank just below the cutting edge.
Polishing of diamond layers for electronic purposes, i.e. diamond layers on flat Si wafers and the like is known from the literature (see e.g. U.S. Pat. No. 5,500,077). The methods applied have been, for example, reactive ion etching using RF plasma generation with different gases such as O.sub.2, CF.sub.4 etc. A highly efficient etching process is described in Llewellyn et. al., SPIE Vol.2286, (1994) 198-204, still only for a two-dimensional set-up. Reactive ion etching (RIE) constitutes a combination of a chemical reaction and physical ion bombardment of a surface. Typical for RIE as compared with plasma etching in general is that the ion energies are high, this due to a low pressure during the process (&lt;100 mTorr).